1. Field of the Invention
The present invention relates to an image reading apparatus for reading an original image using an image sensor such as a CCD.
2. Related Background Art
In known line sensor, a plurality of light-receiving elements of amorphous silicon are aligned along a direction of width of an original so as to photoelectrically read the density of an original image. For example, when an original of A4 size is to be read in an equal size mode with a resolution of 16 pixels/mm along the longitudinal direction (about 300 mm) of the original, a single sensor with about 4,800 light-receiving elements on a 300 mm long substrate is required. However, it is difficult to form such a large number of light-receiving elements, without omissions, on a single substrate so as to provide uniform sensitivity. Therefore, unless the yield of such sensors is improved, practical line sensors cannot be fabricated at low cost.
In order to solve the above problem, line sensor chips each with about 1,000 light-receiving elements are aligned along a scanning direction, and one-line image is read divisionally by the respective line sensor chips. With this arrangement, the number of light-receiving elements to be formed on a single substrate is not so large, and the problems of improved yield and reduced cost can be solved to some extent.
It is, however, difficult to connect end portions of the light-receiving element arrays of the adjacent line sensor chips. When a plurality of line sensor chips are used to constitute a one-line sensor, non-readable regions are fomred.
In order to solve the above problem, a plurality of line sensors are arranged on a single substrate in a checkerboard manner. With this arrangement, nonreadable regions can be eliminated. However, read position error correction between adjacent sensor chips must still be performed.